NAME
strtok, strtok_r
— string token
operations
SYNOPSIS
#include
<string.h>
char *
strtok(char
*str, const char
*sep);
char *
strtok_r(char
*str, const char
*sep, char
**last);
DESCRIPTION
The
strtok()
function is used to isolate sequential tokens in a NUL-terminated string,
str. These tokens are separated in the string by at
least one of the characters in sep. The first time
that strtok() is called, str
should be specified; subsequent calls, wishing to obtain further tokens from
the same string, should pass a null pointer instead. The separator string,
sep, must be supplied each time, and may change
between calls.
The
strtok_r()
function is a version of strtok() that takes an
explicit context argument and is reentrant.
Since
strtok()
and strtok_r() modify the string,
str should not point to an area in the initialized
data segment.
RETURN VALUES
The strtok() and
strtok_r() functions return a pointer to the
beginning of each subsequent token in the string, after replacing the
separator character itself with an ASCII NUL character. When no more tokens
remain, a null pointer is returned.
EXAMPLES
The following will construct an array of pointers to each individual word in the string s:
#define MAXTOKENS 128
char s[512], *p, *tokens[MAXTOKENS];
char *last;
int i = 0;
snprintf(s, sizeof(s), "cat dog horse cow");
for ((p = strtok_r(s, " ", &last)); p;
(p = strtok_r(NULL, " ", &last))) {
if (i < MAXTOKENS - 1)
tokens[i++] = p;
}
tokens[i] = NULL;
That is, tokens[0] will point to
"cat", tokens[1] will point to
"dog", tokens[2] will point to
"horse", and tokens[3] will point to
"cow".
SEE ALSO
memchr(3), strchr(3), strcspn(3), strpbrk(3), strrchr(3), strsep(3), strspn(3), strstr(3), wcstok(3)
STANDARDS
The strtok() function conforms to
ANSI X3.159-1989
(“ANSI C89”).
HISTORY
The strtok() function first appeared in
AT&T System III UNIX and was
reimplemented for 4.3BSD-Tahoe. The
strtok_r() function first appeared in
NetBSD 1.3 and was reimplemented for
OpenBSD 2.7.
BUGS
The System V strtok(), if handed a string
containing only delimiter characters, will not alter the next starting
point, so that a call to strtok() with a different
(or empty) delimiter string may return a non-null value. Since this
implementation always alters the next starting point, such a sequence of
calls would always return NULL.